It has been shown that in the case of a strong pressure accumulation in front of the exhaust gas outlet pipe of the muffler, which is created for example by using a long exhaust pipe connected to the outlet pipe, a portion of the exhaust gas can pass through the mentioned opening into the inside of the enclosure and can here result in undesired side effects, such as thermal overload and/or contamination of the inner chambers of the sound-deadening shroud.
The purpose of the present invention is to avoid such disadvantages by providing a further development of the arrangement which is disclosed in the aforesaid U.S. Pat. No. 4,149,512. This purpose is inventively attained by providing in the annular gap between the exhaust gas outle pipe of the muffler and the wall of the opening in the enclosure at least one cover member, which grips around the exhaust outlet pipe with little play to close the annular gap.